Lives protected by others in combat (6)
I believe the answer is:
resist
'combat' is the definition.
(I've seen this before)
'lives protected by others' is the wordplay.
'lives' becomes 'is' ('be' can be a synonym of 'live').
'protected by' means one lot of letters goes inside another.
'others' becomes 'rest' (I've seen this in another clue).
'is' inserted within 'rest' is 'RESIST'.
'in' is the link.
(Other definitions for resist that I've seen before include "Offer opposition to" , "Use force to prevent something from happening to sister" , "Combat" , "Express opposition" , "Withstand, oppose" .)